How to select the specific frame with object [closed]

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I am detecting the object from the live camera through feature detection with svm , and it read every frame from camera while predicting which affect its speed , i just want that it should select the frame which contain the object and ignore other frames which have no object like empty street or standing car's , it should only detect the moving object

For example , If the object came into camera in 6th frame , it contain into the camera till many frames until it goes out from camera's range , so it should not recount the same object and ignore that frames.

Explanation :

I am detecting the vehicle from video , i want to ignore the empty frames , but how to ignore them ? i only want to check the frames which contain object like vehicle , but if the vehicle is passing from video it take approximately lets assume 5 sec , than it mean same object take 10 frames , so the program count it as 10 vehicles , one from each frame , i want to count it as 1 , because its the one (SAME) vehicle which use 10 frames

My video is already in Background subtraction form

I explore two techniques for it , one is entropy and second is keypoint extraction